Fil Salustri's Design Site

Site Tools


Why Why Why

Given any statement, you can always ask why? In design, asking why? is a simple and surprisingly effective way of uncovering hidden or implied assumptions, issues, and contradictions. The purpose of this method is to get one closer to the root causes of undesired situations. Understanding root causes is important for devising the best possible solution.


The soup

  • Father: Son, you must finish your soup.
  • Son: Why?
  • Father: Because you must have a well-balanced meal.
  • Son: Why?
  • Father: So that you may be able to do whatever you want.
  • Son: Well, what I want to do is throw out this soup.

One might then ask: is there some other way for the father to feed his son, so that he has both a well-balanced meal and enjoys it? This question would not have been obvious if the son had not repeatedly asked why.

Traffic congestion

  • Why do people object to traffic congestion?: Because it causes them irritation.
  • Why does it cause irritation?: Because it delays one unexpectedly.
  • Why are unexpected delays irritating?: Because they force one to alter one's plans.
  • Why do road travellers have plans?: Because the car journey is not an end in itself…or is it?

This chain suggests:

  • The importance of timely and accurate traffic announcements (via, say, radio, or some on-board computer system), as well as systems to help travellers adapt their routes to minimize delays.
  • It can also suggest that some way should be found to let delayed travellers take advantage of the delay to do something important to them – work, entertainment, etc.


  • Why do airplanes fly?: Because the sum of lift and thrust forces exceeds that of the drag and mass forces.

Correct reasoning might proceed as follows

  • Why is that?: Because of Newton's Laws.
  • Why?: There is no why here – this is essentially a root cause.

An example of incorrect reasoning in this case is:

  • Why is that?: Because we designed it that way.
  • Why?: Because we want the plane to fly.
  • Ahah!: A causal loop.


It is interesting to note that when tracing causes through purely physical systems, one generally finds a root cause within 5 Why? questions. It is interesting because it either indicates (a) a rather shallow nature to how the universe works, or (b) a rather shallow sense of the universe on the part of humans. It is left as an exercise to the reader to determine which alternative is the “truth”.

This method is a useful element of failure mode and effect analysis.

design/why_why_why.txt · Last modified: 2020.03.12 13:30 (external edit)